1. Field of the Invention
The present invention relates to a wave absorber and a wave absorber manufacturing method. In addition, the present invention relates to a wave absorber that enables prevention of communication disturbances from reflection and the like of electromagnetic (EM) waves and that enables a thinner and more lightweight product, and to a wave absorber manufacturing method.
This application claims priority from Japanese Patent Application No. 2004-55051 filed on Feb. 27, 2004, Japanese Patent Application No. 2004-265233 filed on Sep. 13, 2004, and Japanese Patent Application No. 2004-371225 filed on Dec. 22, 2004, the contents of which are incorporated herein by reference.
2. Description of Related Art
Due to the development of cell phones, wireless LAN (Local Area Networks), ITS (Intelligent Transport Systems) and the like in recent years, it has become necessary to protect communicated information and to prevent crosstalk and misdirected communications. In the case where protection of communicated information is the primary objective, interception of indoor and outdoor waves is conducted by EM-wave shielding material in order to shield incoming waves and to shield waves emitted from the communications equipment itself. In this case, however, the waves emitted from the communications equipment itself remain in the room due to reflection, causing deterioration in the quality of communication due to the interference of reflected waves with the desired waves for communication. In order to prevent such deterioration in communication quality as well as communication disturbances such as crosstalk and misdirected communications, wave absorbers that absorb waves and convert them to heat are used.
Such wave absorbers use material that is generally capable of converting wave energy to heat and consuming it, and this may be material capable of magnetic loss, dielectric loss and ohm loss. As a wave absorber, a product has been conceived where magnetic powder such as ferrite or soft magnetic metal is mixed and dispersed in an insulating matrix such as rubber or plastic, and molded and processed into sheet form or block form (e.g., see Patent Literature 1).
In addition, as a wave absorber, a product has been conceived where polyurethane foam or the like is impregnated with dielectric loss powder such as carbon black, and processed into pyramid form or wedge form (e.g., see Patent Literature 2).
In addition, as a wave absorber, a product referred to as the λ/4 type has been conceived where resistance film approximately equal to 377Ω, which is the characteristic impedance of free space, is installed at a position that is distant by λ/4 (λ: wavelength of waves at a specific frequency) from a reflector (e.g., see Patent Literature 3).
In addition, wave absorbers have also been conceived where greater thinness and lighter weight are sought by forming periodic conductive patterns on an absorber surface (e.g., see Patent Literature 4), and further where greater thinness, lighter weight and improved absorption properties from oblique directions are sought by forming periodic conducting loops on an absorber surface (e.g., see Patent Literature 5).
Patent Literature 1: Japanese Unexamined Patent Application, First Publication No. 2001-308584
Patent Literature 2: Japanese Unexamined Patent Application, First Publication No. H10-051180
Patent Literature 3: Japanese Unexamined Patent Application, First Publication No. H05-335832
Patent Literature 4: Japanese Patent, Publication No. 3209453
Patent Literature 5: Japanese Unexamined Patent Application, First Publication No. 2001-352191